Cantabrian brown bears shown to deceive rivals in new study

A research team monitored 164 brown bears (Ursus arctos) in the Cantabrian Mountains of northern Spain between 2021 and 2024. Using camera traps at 14 marking sites, they recorded 117,552 hours of footage. Seven male bears – 4.3 % of the sample, including both adults (57.1 %) and juveniles (42.9 %) – were observed climbing trees or using platforms to place chemical and visual marks at a height of about three metres, well above the typical two‑metre maximum reachable while standing on hind legs.

The authors conclude that these bears deliberately inflate the perceived size of their signals to intimidate larger rivals, thereby reducing the likelihood of direct confrontations and potentially increasing reproductive opportunities. The behaviour, documented for the first time in bears, adds complexity to the species’ communication system. The findings were published in the Journal of Mammalogy and involved collaborators from the Spanish National Research Council (CSIC), the FAPAS research institute, several Spanish and European universities, and the Principality of Asturias.

The study highlights a rare but sophisticated form of deceptive signalling among mammals and suggests that such strategies may be more widespread than previously thought.